1. Field of the Invention:
The present invention relates to an energy absorbing member comprising an extrusion made of an aluminum alloy, and having a function that in receiving a compressive impact load or a compressive static load in the extruding axial direction the impact load or the static load can be absorbed.
2. Related Arts:
Recently, the global environment has bee regarded as being of worldwide importance. For example, regulations for reducing gas emissions including carbon dioxide and exhaust gas from automobiles have been strengthened in may countries in order to suppress global warming. Accordingly, lightweight automobiles have been rapidly developed.
Thus, investigations have been made on application of an extrusion made of an aluminum alloy to frames of an automobile and the like.
Into an automobile, incorporated are various energy absorbing members for relieving an impact caused when the automobile collides or contacts another automobile or an object. Recently, attempts have been made to relieve impacts provided to persons in an automobile by using structural members such as a side frame and a bumper stay as an energy absorbing member for absorbing impacts in collision and crushing the member into a form of bellows.
One requirement for such an energy absorbing member is that when a load is applied to the member in the extruding axial direction, in the whole of the member an Euler's buckle (the buckle that the whole of an object is bent into an "L"-like shape) and squeezing cracks (or pressing cracks) do not break out but the member is contracted and deformed into a form of bellows so as to absorb the impact energy stably. When a squeezing crack breaks out, for example, in a side frame of an automobile, contraction and deformation into a form of bellows are disturbed so that energy may not be absorbed stably. Furthermore, broken pieces are scattered in a small engine room and a tip of the pieces is projected out to damage other parts and wirings or penetrate through an outer plate of the car body. Thus, such a material cannot be regarded as a reliable material.
Hitherto, various investigations have been made on development of members having a stable energy absorbability. For example, Japanese Patent Laid-Open (JP-A-) No. 6-247338 discloses a technique of intentionally making different between the sectional secondary moment (rigidity) around the X axis and that around the Y axis in the cross section of a side member comprising a hollow member having a rectangular section, in order to cause the hollow member to be contacted and deformed into a form of bellows, with Euler's buckle being restrained; and setting the section shape of the panel, in the side member, which may be probably buckled into a form of bellows into such a shape that after collision of the panel, the panel will be buckled previously to buckles of other panels. This publication states that once any one of panels is buckled, the buckle into a form of bellows is transmitted to other panels in succession, and that even if the whole of the side member is long, the buckle into a form of bellows occurs stably over the whole length. Besides, JP-A-6-25783, JP-A-7-118782, JP-A-7-310156, JP-A-8-216917, JP-A-8-310440 and others disclose a technique for improving energy absorbability by investigating and adjusting the composition of an aluminum alloy for use as an energy absorbing member, and its structure.